Ammeter for standby generator

Thread Starter


Joined Jun 2, 2006
I would like to build an ammeter for monitoring the load on a “whole-home” standby generator.

The generator is single-phase and has a rated maximum power of 12 kW (15 kW surge) and rated maximum load current of 50 Amps at 240 Volts and 100 Amps at 120 Volts.

The automatic transfer switch (ATS) has load sensing, as well as load shedding capabilities. There are two dry contactors on the ATS that control relays for the air-conditioning (terminals A-A) and a 90 Amp sub-panel (terminals B-B ). Terminals A-A have precedence over terminals B-B, which shuts down the 90 Amp sub-panel so the air-conditioning can start. Air-conditioning is wired to the generator sub-panel.

Yes, this all work great. The problem is there is no ammeter to see how much load is on the generator.

I would like to accomplish two tasks; 1). balance the load on each leg of the generator, and 2). put as much stuff on the 90 Amp sub-panel as the generator will allow.

My current thought (no pun intended) is to use 2 current transformers wired to 2 panel meters.

Could it be this simple? Will a 100:5 CT wired to a compatible panel meter do the trick without any other circuitry? Will the panel meter bounce around at 60-cycles or is this controlled by the CT or meter?

Other than basic math, can I indicate the total load on a seperate panel meter? If yes, how?

In advance, thank you.

Erin G.

Joined Mar 3, 2005
If you only need to "see" the amps during your setup and load balancing, and don't need a contiuous display, why not buy a cheap clamp-on amp meter? Lowes has a few for under $80. You move your clamp-on to the conductors you want to meter one at a time until your trouble shooting / balancing is done. Then you have a portable amp meter left over that you can use anywhere you need to.

If you do need continuous monitoring, or you're just a project person who wants to set up permanent meters, then thingmaker3's suggestion is perfect.


Joined May 19, 2004
1. balancing a residential single phase system with two 120vac legs is very difficult, as loads are continually changing. the 240v loads are as balanced as they can get without rewiring the appliances themselves, so it's primarily the 120v loads that you are trying to even out. so it requires some planning as to what loads are typically on at the same time throughout the day, bearing in mind that heating elements and motors typically can be the highest draw in the home.

2. if you are attempting to install permanent ammeters, there are many commercially available on the market when you search. and likely even from the ats manufacturer, which ususlly have them built in, at least on the ones i have installed.